Using the terminology we intro-
duced earlier, we might then say that black and white squares are in comple-
mentarydistribution on a chess-board. By this we mean two things: firstly,
black squares and white squares occupy different positions on the board: and
secondly, the black and white squares complement each other in the sense that
the black squares together with the white squares comprise the total set of 64
squares found on the board (i.e. there is no square on the board which is not
either black or white).